Another U.S. spacecraft has landed successfully on Mars to begin a three-month search for traces of ancient water. It has deployed itself and begun transmitting its first images of the surrounding terrain, never seen before. Engineers are making progress fixing the malfunctioning Spirit that arrived earlier in the month.

Pandemonium broke out at mission control in California when the Opportunity spacecraft endured a fiery descent through the Martian atmosphere to land safely on target halfway around the planet from the Spirit rover already there.

The manager of the landing phase, Rob Manning, cheerfully and succinctly confirmed the touchdown. "We're on Mars, everybody!" he announced.

Like Spirit three weeks ago, Opportunity's descent signals showed that it deployed a parachute and fired braking rockets to slow its 20,000 kilometer per hour entry speed, then inflated airbags to cushion its landing.

Navigation team member Louis D'Amario said the landing was on target within a cigar-shaped area 74-by-5 kilometers. "It looks like that we hit the bull's-eye again with Opportunity, just like for Spirit," he said.

At a jubilant news conference, NASA administrator Sean O'Keefe toasted with champagne, as he had done three weeks ago when Spirit landed.

"As the old saying goes, it's far better to be lucky than good," he said to the laughter of his colleagues, "but you know, the harder we work, the luckier we seem to get."

The goal of Opportunity, like Spirit, is to seek signs that water once flowed on Mars, an indication that it might have supported life. While Spirit landed in a crater scientists believe is an ancient lake bed, Opportunity is on a high, flat plain with rich deposits of a mineral called hematite, known to form in association with water.

Hours before Opportunity's touchdown, mission engineers described progress in fixing what they believe is a computer software problem that has interrupted Spirit's science operations.

Project manager Peter Theisinger suggests that part of the vehicle's computer memory is faulty and predicts that technicians can work around it to rely on another part of the memory. He says his team does not yet know what caused the computer software problem, but adds that they have been able to regain command over the malfunctioning rover and might get it back to work in three weeks.

"Twenth-four hours ago, I sat up on this stage and told you that we had a serious problem with Spirit," he said. "Here we are tonight with Spirit, we think, on a path to recovery and we've successfully landed Opportunity on Mars. I think we've been surprised how well it has gone."

Mission officials say Opportunity bounced to an upside down landing, but has already made itself upright, opened its petals like a flower, and deployed its solar energy panels and antenna.

NASA's chief of space science, Ed Weiler, said the agency's Mars landing record has now improved, with five of six attempts since the 1970s successful. He praised engineers' efforts to resuscitate the Spirit rover. "I came here prepared for a funeral, basically, and instead we resurrected one rover and we saw the birth of another today," he said.